Combination crude distillation and cracking process



Jan. 17, 1956 c. T. HARDING ETVAL 2,731,396

COMBINATION CRUDE DISTILLATION AND CRACKING PROCESS Original Filed June 3, 1950 5 Sheets-Sheet l 92 fue 7, Hardw g 7%@ D Clbbcrne Jan. 17, 1956 c. T. HARDING ETAL 2,731,396

COMBINATION CRUDE DISTILLATON AND CRACKING PROCESS Original Filed June 5, 1950 5 Sheets-Sheet 2 Priooo dT FRA-TIQMATOQ STQIPPEQ F1a-1A Jan. 17, 1956 Original Filed June 3, 1950 C. T. HARDING ET AL 2,731,396 COMBINATION CRUDE DISTILLATION AND CRACKING PROCESS 5 Sheets-Sheet 3 czf'Ze T Hardin fla Clbborae Jan. 17, 1956 c. T. HARDING ET AL 2,731,396

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COMBINATION CRUDE DISTILLATION .AND CRACKING PROCESS Original Filed June 5, 1950 5 Sheets-Sheet y5 )CYSczr'Ke T Hardin 'auree dime r avent rs Rza/:ard O. Wig/'25 s o Qbbocneg United States Patent O HC CMBINATIN CRUDE DISTILLATION AND CRACKING PROCESS Clarke T. Harding, Hillside, Maurice W. Mayer, Summit, and Richard 0. Wright, Cranford, N. il., assignors to Esso Research and Engineering Company, n corporation of Delaware Original application .lune 3, 1950, Serial No. 165,982, now Patent No. 2,644,785, dated `luly 7, 1953. Divided and this application July 30, 1952, Serial No. 3tl1,716

l2 Claims. {CL 19d-49) The present invention relates to the conversion of crude petroleum into more valuable mineral oil products. `More particularly, the invention is concerned with an improved process for obtaining maximum yields of high quality low boiling products of the motor fuel and heating oil boiling ranges and desirably low yields of heavy products, such as fuel oils and tar with a minimum of treating steps and a substantially reduced investment and operating cost. ln its broadest aspect, the invention involves a series of integrated distillation and catalytic conersion stages wherein products from said stages are conducted to a product fractionation stage and treated therein in such a manner that reduced crude obtained as liquid residue of a crude distillation stage is stripped with product vapors obtained in the crude distillation and/or conversion stages and all desirable fractions produced, such `as motor fuel and heating oil and all the less desirable heavy material, such as fuel oil fractions, are recovered in optimum relative proportions and quality. More specilically, the invetion pertains to combination processes of this type wherein one of the conversion stages is catalytic reforming of naphtha, particularly in the presence of hydrogen. The present application is a division of application, Serial Number 165,982, filed June 3, 1950, now U. S. Patent 2,644,785, for Clarke T. Harding, Maurice W. Mayer and Richard O. Wright, entitled Combination Crude Distillation and Cracking Process.

ln conventional combination crude oil distillation and `conversion processes the recovery of maximum yields of motor fuel and heating oil products has been usually desired, to suitable thermal or catalytic refining treatments, such as reformation, isomerization, hydroforming, alkylation, etc., thermally or catalytically cracking a gas oil fraction from the crude still to recover further low boiling products by subsequent fractionation of the cracked products and subjecting the reduced crude to a further distillation at reduced pressures to produce tar and additional low boiling products, principally gas oil to be processed with the gas oil fraction from the crude still as mentioned above. These processes normally require as many product fractionators as there are conversion stages, yielding a plurality of streams of products of desirable boiling range. For economic heat recovery, large numbers of heat exchange apparatus are required both within each unit and in combination between units. Vast tank facilities must be provided to permit storage of the various products prior to blending in desired proportions. The vacuum distillation equipment normally used for working up the reduced crude is expensive with respect to investment, operation and maintenance. As a result of these complications, conventional type combination processes must be operated on a relatively large scale to be economical. In most cases, refining capacities in excess of, say, about 20,000 bbl/day of crude are required to make operations of this type pay while smaller refineries must be designed on the basis `of an often undesirably 2,731,396 Patented Jan. 17, 1956 high output of heavy fuel oil and other products of a realtively low commercial value.

The vacuum still for reduced crude distillation may be eliminated to realize substantial savings in fractionation equipment and tankage facilities by supplying substantially all the vaporous products of the various stages of a combination process as well as the reduced crude from the crude distillation to a single product fractionation stage and using these vapors to strip the reduced crude in the fractionation stage of all its distillable constituents. in this process the crude oil is subjected to distillation in a conventional crude distillaton unit to produce an overhead stream of light virgin naphtha, a separate heavy naphtha stream, a still heavier stream of the kerosene and Diesel oil range and reduced crude bottoms.

The reduced crude is passed directly to an upper portion of the lower contacting section of a substantially conventional fractionating column. The heavy naphtha stream is subjected to high temperature reforming or other conversion conducive to an improvement of its motor fuel qualities. The total vaporized effluent from this conversion stage is fed to the fractionating column at a point below the feed point of the reduced crude, substantially at the temperature of the conversion stage.. The light virgin naphtha may enter the fractionating column likewise at a point below the reduced crude feed point after suitable additional heating, if desired. Various final product streams are recovered from the product fractionator which may include a fuel gas overhead, a low boiling fraction of the motor fuel boiling range, a heating oil fraction, a gas oil fraction, and a heavy bottoms fraction of the fuel oil range. Part of the gas oil fraction is passed to a catalytic cracking stage to be converted therein into additional amounts of motor fuel, Diesel oil, gas oil range cycle stock and heavy bottoms. The eifluent of this stage is passed to the product fractionator likewise at a point below the reduced crude feed. ln this manner, the reduced crude or equivalent thereof is subjected to countercurrent heating, vaporization and stripping actions with vapors from the gas oil cracking process as well as with the virgin and reformed naphtha vapors.

When operating substantially in the manner described above, extremely large volumes of process vapors are available and may be utilized for reduced crude stripping with the effect that the volume of heavy fuel finally produced may be kept at a minimum at least as low as and, if desired, even lower than it may be accomplished in conventional operation involving vacuum distillation of reduced crude. The total product naphtha is prepared as overhead product which has been maintained at high temperatures for a minimum time and is, therefore, -of superior quality with respect to gum and color stability. A single heavy fuel fraction is obtained in which all heavy constituents formed in the various stages may be combined and which may be subjected to a single ltering treatment to recover a nal low sediment fuel oil of best quality. These advantages are in addition to the .obvious savings of heat exchange `equipment resulting from the elimination of various intermediate heating and `cooling operations and to those of intermediate tankage .requirements resulting from the use of a single product fractionation stage.

In the type of operation described above the yield and quality of the motor fuel fraction recovered suffer to a certain extent from the fact that thermal reforming or catalytic reforming in the absence of substantial amounts of hydrogen must be used rather than catalytic hydroforming in the reforming stage to afford an eilicient operation of the product fractonator. Catalytic hydroforming or similar processes are far superior to reforming processes carried out in the absence of hydrogen, with respect to product quality including the yield-octane number relationship, sulfur content and engine cleanli-` ness of the gasoline. However, processes of this type involve a net production and recycling of large amounts of hydrogen. Introduction of this hydrogen together with the reformate into the common product fractionator would seriously interfere with the recovery of valuable hydrocarbon light ends or require a fractionator design of uneconomical dimensions. I

The present invention overcomes this difficulty and affords various additional advantages as will be apparent from the description below wherein reference will be made to the accompanying drawing.

In accordance with the present invention, catalytic reforming of naphtha in the presence of hydrogen is integrated into a simplified combination process of the type specified above wherein reduced crude is injected into a combined product fractionator and reduced crude stripper together with vapors from other process stages which vapors serve to Strip the reduced crude, at least a substantial portion of the hydrogen produced in the reform- 'ing operation being used to treat suitable hydrocarbon fractions -of the combination process, outside the reforming stage and the combined fractionator-stripper. The preferred modification of the invention involves the incorporation into said simplified combination processof catalytic naptha reforming operations of the type known as platforming wherein virgin and/or cracked naphtha is contacted with a platinum catalyst at elevated temperatures of about 8001000 F., high pressures of about 400-1000 p. s. i. g. and relatively high hydrogen recycle rates of about 3000 to 12,000 s. c. f./bbl. maintained by recycling hydrogen produced in the process. Processes of this type and suitable catalysts therefor are known in the art (see for instance U. S. Patents Nos. 2,478,916; 2,479,109; 2,479,110; Petroleum Processing, vol. 5, No. 4, pages 351-360). At the conditions specified, three major reactions occur, namely dehydrogenation of naphthenes to 'the corresponding aromatics, hydro-cracking of high molecular weight hydrocarbons into saturated hydrocarbons of lower molecular weight and isomerization of naphthas and straight-chain hydrocarbons. In addition, there takes place dehydrocyclization of straight-chain hydrocarbons directly into aromatics and desulfurization converting substantially all sulfur into hydrogen sulfide. 'Chiey as aresult of the high hydrogen partial pressure the catalyst retains its lactivity for many months without regeneration.

Other conventional hydroforming processes may be used for the purposes of the invention. For example, the virgin and/ or cracked naphtha may be contacted in the presence of extraneous hydrogen and/ or hydrogen formed in situ with such well known catalysts as the oxides of molybdenum, aluminum, vanadium and tungsten, with or Without silica, supported on alumina or cobalt molybdate assuch or molybdena supported on zinc aluminate, etc. at temperatures of about 800 to 1000 F., pressures of about 50 to 1000 p. s. i. g. and gas recycle rates of about 1000-3000 standard cu. ft. per bbl. of a recycle gas containing about 80% H2. Continuous or intermittent regeneration of the catalyst may be employed, if necessary, to remove carbonaceous deposits by controlled burning with air in mixture with recycled iiue gas from Vthe regeneration process. Regeneration temperatures are generally limited to 10001200 F. at any convenient pressure. AThe platforming or otherr conventional hydroforming treatment may be effected in fixed bed, moving bed, fluidv or suspensoid type of operation, all in a manner known per se.

When incorporating such catalytic hydroforming processes into a simplified combination process of the type specified above in accordance with one embodiment of the present invention, hydrogen made available in the hydroforming stage is used to upgrade cracked fractions withdrawn from the combined fractionator-stripper by an upgrading treatment involving hydrogenation. For ex- CII ample, any desired. Portion Qf the sas Oil recycle Steck may be treated either with hydrogen separated from'the reformer eftiuent or with the total reformer efiiuent. The treatment with hydrogen may be carried out at noncracking conditions including temperatures of about 500 to 900 F. and pressures of about 750 to 4000 p. s. i. g. in the presence of conventional hydrogenation catalysts, such as the oxides or sulfdes of groups V, VI and VIII heavy metals. Such hydrogenation improves the quality of the recycle stock as a catalytic cracking stock by hydrogenating coke-forming constituents such as polycyclic aromatics prior to cracking.

The hydrogen from the hydroforming-stage may also be used to upgrade product light cracked gas oil within the heating or Diesel oil boiling ranges. For this purpose the type of product oil mentioned may be hydrogenated on the catalysts of the V, VI and VIII groups just mentioned at either substantially desulfurization conditions such as temperatures of about 500-800 F. and pressures of about -5.00 p. s. i. g., or substantially hydrogenation conditions Similar to those described with reference to the hydrogenation of gas oil recycle stock, Rather than .using Separated hydrogen, the total hydroforrner efiiuent may be used to'upgrade the light cracked product gas oil as will appear more clearly hereinafter.

The reformed naphtha may be blended with the naphtha fractions recovered from the fractionator-stripper, preferably after the latter have been subjected to conventional finishing treatments such as caustic washing and/or suitable sweetening processes known to the art. The reformed .naphtha ,itself is of such high quality and purity as not to require further nnishing of this character.

While these types of operation may require special gas-liquid separation and/ or fractionation means in addition to the Vcombined fractionator-stripper, the resulting increased investment is at least in part compensated by the improvedquality of the final motor fuel blend. Furthermore, the naphtha finishing equipment may be substantially .reduced in size whereby appreciable savings in investment are secured.

In accordance with another embodiment of the invention the totalefiluent of the catalyticrnaphtha hydroforming stage including all the hydrogen present in this stage is used without intermediate cooling to strip at least a portion of the reducedcrude prior to its entry into the combined fractionator-stripperin a separate stripping stage operated substantially at the pressure of the hydroforming stage.- Assuming a temperature of the reduced crude recovered from the crude still of about 600k to 750 F. and atemperature of about 800-1000 F. of the hydroformer effluent this preliminary stripping may take place over a temperature range of about 650 to 800 F. at alpressure of about 100 to 1000 p. s. i. g. At these conditions, a substantial proportion of the gas-oil and lighter constituents of the reduced crude, say about 5 to 50%, will go overhead with the hydroformate and hydrogen. Hydrogen may then be separated from normally liquid overhead and recycled to the hydroforming stage after suitable reheating. The hydroforrnate containing Vthe reduced crude strippings may be passed to the fractionating section of the combined fractionator-stripper or fractionatedin a separate tower to produce gas oil to be used as catalyticfcracking stock and product hydroformate whichmay be blended with the finished naphtha from lthe combined Vfractionator-stripper as described above. The 'prestripped reduced crude is passed'to the stripping section of the combined fractionator-stripper to be further-stripped therein with the efuent vapors of Vstripping section of thecombined fractionator-stripper to .assist in strippingreduced crudetherein.

The naphtha to `be .hydrofonned `may rb efeither virgin heavy-naphtha alone or heavy naphtha withdrawn from the combined fractionator-stripper and containing both virgin and cracked naphtha or any suitable mixture of such heavy naphthas. lt may be desirable to make all virgin naphtha available for stripping the reduced crude in the cornbined fractionator-stripper. ln this event a combined virgin light and heavy naphtha stream may be passed directly to the stripping section of the fractionator-stripper and only a heavy naphtha fraction from the fractionator-stripper may be subiected tocatalytic hydroforrning as described above.

.Having set forth its general nature and objects, the invention will be best understood from the more detailed description hereinafter which refers to the accompanying drawing wherein Figures 1 and 1A show a schematic dow plan of the combination process in accordance with the invention;

Figure 2 illustrates semi-diagrammatically and in greater detail a catalytic cracking system of particular utility for the combination process of the invention; and

Figures 3 and 4 illustrate in a similar manner preferred embodiments of the hydroforming section of the system of Figure 1.

Referring now in detail to Figures 1 and 1A of the drawing, the system illustrated therein essentially comprises a crude still 10, a catalytic naphtha hydroforming stage schematically shown by element 30, a combined product fractionatorripper 40, a cracking stage schematically illustrated by element 50, and fuel oil filtering facilities at 90. The functions and coaction of these elements will be forthwith explained using as au example the refining of a medium gravity crude of the type of Arabian Qatar crude in a refinery having a capacity of about 10,000 bbl. of crude per day. It should be understood, however, that the system may be used for the relining of different types of crude at a larger or smaller scale in a generally analogous manner.

in operation, the crude oil is pumped from line 1 by means of pump 3 via line 5 through heat exchangers 6 to a heating coil located in furnace 7 wherein it is heated to a temperature suitable to vaporize a substantial portion of the oil. The oil so heated is passed through line 9 to a lower portion of still 10 which it may enter at a temperature of about 600-800 F. and a pressure of about 4070 p. s. i. g. Still 10 may be provided with a plurality of horizontal bubble cap plates l2 to improve fractionation of the feed in a conventional manner. Reflux may be accomplished with the aid of partial condenser 14 arranged in the top of still 10. For the purposes of the present example, still 10 may be so operated that three distillate streams and distillation bottoms are produced as follows.

All crude constituents boiling below about 250 F. are removed together as a vapor stream of light virgin naphtha overhead through line 16 at a temperature of about MHV-350 F. This stream may amount to about Z0-25% of the crude charged. A liquid stream of heavy naphtha having a boiling range of about 250400 or 500 F. is removed through line 1S from an upper portion of still 10 below condenser 14. About 1Z0-25% of the crude charged is ,recovered through line 1li. keroseno or Diesel oil cut boiling within the range of about 400-700 F. and amounting to about l7-23% of the crude is drawn off through line 20. The remainder of the charge, amounting to about 40-50% and consisting predominantly of constituents boiling above 700-800 F. is withdrawn as reduced crude through line 22 from the bottom of still l0. The kerosene cut removed through line is normally suitable for kerosene or Diesel oil purposes without further treatment and it. may be passed directly to storage. The other fractions may be treated in accordance with the present invention as wiil be forthwith described.

The light virgin naphtha vapors in line 16 may be passed directly to a lower portion of product fractionator 40. If desired, this vapor stream may be preheated to about 800-l000 F. to conform with the heat requirements of fractionator 40. This may be done by by-passing at least a portion of the vapors in line 16 through a heat exchanger 1'7 in indirect heat exchange with hot products from hydroforming stage 3l) operated as will be described hereinafter.

The heavy naphtha stream may be pumped by pump 26 through line 2li at a pressure of about 60G-900 p. s. i. g. to a catalytic hydroforming stage 30. This hydroforrning may be of any conventional design well known in the art suitable for a platforming operation or a regenerative hydroforming operation of the type specified above. Equipment suitable for this purpose will be decribed below in greater detail with reference to Figures 2 and 3. For the present example, a conventional catalytic reforrnin7 operation carried out at about 800 to 1000 F., 50 to i000 p. s. i. g. pressure, nominal oil residence time of about 0.5 to 2.5 hours calculated as cold oil in contact with catalyst, and hydrogen recycle rates of about 500 to 7000 s. c. f./bbl. of oil using al catalyst, such as molybdena supported on alumina, in fixed bed operation is referred to. In addition to the virgin naphtha supplied to hydroforming stage 30 via line 28, a hydrocarbon stream of similar boiling range derived from the fractionator section of tower l0 may be fed to hydroforming stage 30 via line 2@ in any desired proportion. At the conditions specified the octane rating of the naphtha may be increased from about 25 to 40 to about 80 to 100 Research Octane Number without excessive cracking to normally gaseous hydrocarbons and carbon. A plurality of hydroforrning reactors may be provided alternating between onstream and regenerating cycles, oxidizing gases such as air, steam, flue gases or mixtures thereof, being used in the regenerating cycle to remove carbon from the catalyst all in a manner known per se. Of course, any type of continuous operation such as fluid, moving bed or suspensoid operation may be used wherein the catalyst is continuously circulated between reactor and regenerator vessels. lf desired, extraneous hydrogen may be supplied to hydroforming stage 30 via line 31.

The total effluent of hydroforrner 30 is passed through line 34 via heat exchanger 17 to a stabilizer tower 100 wherein hydrogen and normally gaseous hydrocarbons such as Cr-Ca hydrocarbons are separated from normally liquid hydroformate at temperatures of about to 120 F. and pressures of about to 1000 p. s. i. g.

Gases containing about 40 to 90% of hydrogen and amounting to about 1000 to 9000 s. c. f/bbl. of feed are withdrawn from stabilizer 100 through line 102 and passed through recycle booster 104 and reheater 106. An amount corresponding to about 500 to 7000 s. c. f. of hydrogen per bbl. of feed may be passed via line 108 to hydroformer 30 substantially at the temperature and pressure of the latter. The remainder of the gases in line 102 or any desired portion thereof may be passed through line 110 via booster 111 and lines 112 and/ or 114 to hydrogenation stages 116 and/or 118 which may be used to improve the cracking characteristics of cracking recycle stock supplied from tower 40 through line 42 or to improve the quality of product light gas oiil recovered from tower 40 via line '7E as will appear more clearly hereinafter. Any excess gases may be withdrawn through line 103 and passed through line 103a to the bottom portion of fractionator-stripper itl as an additional stripping agent or used as fuel gases in the system. When operating in this manner for example, the gravity of recycle gas oil can be increased 2-15 degrees, and the stock made as desirable as is virgin feed for catalytic cracking.

The hydroformate separated in stabilizer 100 is Withdrawn through line 12.0. This material may be blended without further treatment in tank 122 with finished gasoline recovered from tower 40 as will appear more clearly hereinafter. The hydroformate so recovered may amount to about 10 to 25% on crude.

mousse Returning no w to the reduced crude in line 22, this stream may be passed directly to the lower portion of fractionator 40, `substantially at the temperature of its withdrawal from still 10. Line 22 feeds into fractionator 4t) at a point above the feed point of line 16. In this manner, the vapors supplied through line 16 pass upwardly through fractionator against the downwardly flowing reduced crude to strip the latter of vaporizable constituents. This effect and the operation of fraction ator 40 will be described in greater detail later on.

At this point it is noted that a side stream of gas oil range hydrocarbons amounting to about -60% on crude and boiling between about 600 and 1000 to 1l00 F. which is suitable as a catalytic cracking stock, may be withdrawn from an intermediate section of fractionator 40 via a gas oil reux system comprising purnp 43 and lines 42, 44, and passed eithervvia line 44a or through hydrogenation stage 116 which will be described below, to line 46 and a catalytic cracking stage 50. Any conventional cracking system adapted to convert gas oil range hydrocarbons into lower boiling oils, particularly of the motor fuel range, may be used. Continuous or batch operation may be employed in fixed bed, moving bed, fluid or suspensoid systems. Heat required for cracking may be supplied as preheat of process materials and/or as sensible heat of exothermically regenerated catalyst or in any other conventional manner. Modified natural or synthetic clay or gel type catalysts such as activated montmorillonite clays, silica-alumina, silicamagnesia composites and other conventional cracking catalysts may be employed at temperatures of about 800-1000 `F. and pressures of about atmospheric to 25 p. s. i. g., all in a manner known per se. A cracking system offering particular advantages in connection with the Apresent invention will be described in greater detail later on with reference to Figure 2 of the drawing.

The total hydrocarbon Veiliuent of cracking stage 56 is passed substantially at the cracking temperature of, say, about 800-1000 F. through line 52 to the lower portion of fractionator 40, preferably at a point intermediate between the feed points of the reduced crude on the one side and of the virgin naphtha on the other side. If cracking stage is operated at an elevated pressure, the pressure may be released by valve 52a to fractionator pressure. In most cases, about 95-l00% of the cracked material enters fractionator 40 in the vapor state to enhance the stripping action of the vapors supplied through line 16, while `any unvaporized constituents of the cracked material are in turn subjected to stripping by those vapors introduced through line 16.

As indicated Airri-"i'ure lA, fractionator ai@ comprises a lower stripping section A and an upper combined fractionation-absorption section E. Both sections are provided with suitable means forimproving the countercurrent contact between downowing liquid and upwardly flowing vapors. For the purpose of stripping, a disc-and-doughnut baille arrangement has been found to be most eicient and such is shown scL ematically for section A by elements 4i. Section B is illustrated to contain a number of bubble cap plates 5d to enhance the etiiciency of the fractienation-absorption process. Sections A and B may operate as follows.

Stripping section A receives, aside from the vapor and liquidV streams supplied through Vlines 16, 52 and 22, a liquid top feed comprising a gas oil out removed from the' bottomof'sectionV B via line 42 and suppiied to section'A via line d4.y This gas oil is fed to section A to provide control over the reflux and heat removal in that section in order to obtain the desired end point and ,clean up on the gas oil. All the heat required for stri ping and fractionation in fractionator fst) is preferably supplied total heat, e., sensible plus latent heat of the hydrocarbon streams entering section A to maintain a temperature of, say, about.82:()5836o F. in the lowest portion of section A. The vapors rising through section A strip the downwardly bwing gas oil cut, 'reduced crude and cracked liquid products of substantially ali their distillable constitutents and this vapor mixture passes on at atemperature of about 7GQ750 F. into frac tionationabsorption section B to be treated as will be described later on.

The reduced crude from line 22 which may contain as much as about 75% of gas oil suitable for feed to the catalytic unit is countercurrently stripped and heated by the cracked vapors, at say, about 875 F. and 8 p. s. i. g. and then by the virgin naphtha vapors at, say about 890 F. The partial pressure effect of the other streams and the heat content thereof are suflicient to cause the gas oil constituents of the reduced crude to vaporize Vand to supply the required heat. The net effect ofthe process in section A then is (l) a bottom stream of uniiuxed fuel oil amounting to about 10-l5% on crude and consisting of ashed reduced crude containing about 0.3% of heavy slurry oil from the catalytic operation, blended autoinaticaliy so that it may be flux'ed with about 50% of light diesel oil blending stock for fuel oil viscosity correction; (2) vapors containing all of tne distiliate products to be obtained from fractionator 4t) and leaving section A overhead at about 800 F.

A heavy material containing all the non-distillable constituents of the crude charged and of the fractions converted in stages 30 and 50 collects at about S2W-830 F. in the bottom zone of section A from which it may be withdrawn via line 47. If desired, the temperature in the bottom of section A may be reduced to, say, about 700 F. by recycling heavy bottoms from tine d? by means of pump 49 via cooler 53 and line rfhe bottoms quenching may be desirabie to prevent cracking and coking of the heavy liquid products. Combined reduced crude amounting to about 10 to 15% on crude may be recovered through line $1 to further treated as will appear hereinafter.

At the conditions of the present example about 500 to 1009 niels/hr. of hydrocarbon vapors will be avail-` abie to strip in section A about 109-20G niels/hr. of liquid. This favorable vapor-liquid ratio results in efficient stripping in section A. The number of disc-and doughnut baiiies and the dimensions of section A depend largely on the character of the crude charged and the products desired. For the purposes of the present eX- ampie, this section may be approximately 12 in diameter and 30 in height and is equipped with 7 sets of discand doughnut type contacting devices. Whenever the vaporliquid ratio in section A is undcsirabiy iow, the operation of crude still 1) may be changed so as to take a wider naphtha cut or even Vall the light and heavy virgin naphtha overhead through line 16 to increase said ratio,

while correspondingly increasing the proportion of naphtha supplied to'hydroformer 3Q from tower 45 via line 29. In an extreme case, the entire naphtha feed of hydroformer 30 may be so supplied from tower 4b without substantial changes in the operating conditions described above.

Vapors passing upwardly to section B. of the fractionator 4d are fractionated with gas oil redux through line 44 and cooler 4S. Gas oil may be withdrawn through line 42 atv about 650-750 F. and may be divided into 3 streams, namely (1) reux through line d4 as described; (2) a liquid product arnounting'to about .l5-3% on crude for heavy Diesel oil 'blending through line 48 andV vasrefluii to fractionator via line `44 may -be supplied by pump 43 to hydrogenation stage 116 and hydrogenated therein on nickel tungsten sulde as the catalyst at a temperature of about 7 50 to 800 F., a pressure of about 2500 to 3000 p..s. i. g., a liquid throughput of about l to 2 v./v./hr. and a hydrogen feed rate of about 2500 to 3000 standard cu. ft. per bbl. of oil in fixed bed opera tion. At these conditions about l000-l200 standard cu. ft. of hydrogen per bbl. is consumed in the hydrogenation operation. The All! gravity of the heavy cycle gas oil is increased by about lll-l2 units and substantially all sulfur is removed. The hydrogenated gas oil may then be passed on through line lo as described above.

Passing now to section B of fractionator 40, it is noted that in most conventional catalytic cracking and similar refining operations, products are fractionated at low pressures to produce a gas and low pressure distillate. The gas stream contains appreciable quantities of gasoline constituents and it is, therefore, necessary to compress, absorb, and refractionate this stream to recover its gasoline constitutents. This may be avoided by combining both low pressure absorption and fractionation in the upper section B of fractionator 40. For this purpose, one of the pumparounds normally used merely for heat removal .and returned to a point close to its withdrawal may be used as an absorption medium by returning it to a point substantially above that from which it is withdrawn.

The operation of the upper part of section B is disclosed and claimed specifically in the copending Rich et al.

application Serial No. 153,332, filed April l, 1950, and 9 assigned to the same interests. It will be brieliy described herein insofar as it contributes to the essential advantage claimed for this invention, which resides in making small refineries fully competitive with large re iineries. For specific details said copending Rich et al. application is here referred to.

Product vapors leaving the gas oil fractionating section and entering the heating oil withdraw plate contain heating oil, naphtha and gas. In the section immediately above the heating oil withdrawal line 56, these product vapors which may be at about l0520 F. are cooled by contact with cool heating oil at about 130 F. entering the tower through line 68. Heating oil is condensed out and falls along with the cooled part entering through line 68 and both are withdrawn from the tower through line 56. The cool heating oil in line 68 is saturated with C5, C4 and C3 homologues to form a fat oil. The light fractions are stripped out by ascending naphtha and gas product vapors, thus increasing the concentration of said fractions in the naphtha condensing zone and increasing the absorption thereof in the naphtha.

Light gas oil is withdrawn at about 48m-500 F. through line S6, most of it being cooled in cooler 5S and returned to the top of section B by pump 60 and line 62 as absorber lean oil, the remainder being stripped in stripper 57 and taken through line 78 to flux via line 83 and product via line 119, vapors being returned through line 59. Any desired portion of the stream in line 7a3 may be passed through hydrogenation stage lllfi to be treated therein with H2 supplied via lines 110 and 11d.

For this purpose, the light gas oil in line 73 may be supplied by pump '79 to hydrogenation stage 11S and hydrogenated therein for example, on nickel tungsten sulfide as the catalyst at a temperature of about 700 to 800 F., a pressure of about l'75 to 225 p. s. i. g., a liquid throughout of about 0.75 to 1.25 v./v./hr. and a hydrogen feed rate of about 800 to 1200 standard cu. f. per bbl. of oil in fixed bed operation. At these conditions hydrogen consumption in this operation is about 200 to 300 standard cu. ft. per bbl. and the light gas oil recovered through line 80 will be substantially completely desulfurized.

Product vapors entering the portion of section B which lies above the inlet of line 68 thus consist of the naphtha fractions and gas fractions normally encountered plus an abnormal quantity of C4, C5, and Ca which were absorbed 1.0 as previously explained in the top of section B. Such vapors and heating oil are fractionated by reflux pumped back through line '76 and the fractionated vapors may be taken from the tower at about 5 p. s. i .g. and 215 F. through line 66 and may be compressed by a one stage blower 69. Naphtha with an excess of light fractions is condensed in condenser 72, stripped of the excess light fractions in stripper '73 and, except for the part returned as reflux7 through line 76, sent to final product tankage through line 70.

Gas and iight fractions are led back to the absorber portion of section B through line 77 where countercurrent absorption of the desired light fraction by the lean oil as previously described takes place. The number of plates between lines S6 and 62 is preferably increased by about 10-15 over that of normal fractionator designs. vlI-y using this technique it is possible to absorb essentially all of the Cs-lfractions in the gas entering the top section of fractionator 40. in addition, as much as 75% of the C4 components can be absorbed. The gas leaving the top of fractionator 40 through line 64 is thus stripped of its valuable gasoline components and can be passed directly to fuel uses. A naphtha or gasoline cut may be recovered vla line 6d. Such gasoline can be withdrawn at temperatures of about l20l50 F. in spite of the low pressure employed. if the crude is such or the distribution of products so demand, it is possible to operate section A at pressures below that in the absorbet` portieri in the top of section B-say 5-l5 p. s. i. in order to permit reduction of crude to very low bottoms, while at the same time obtaining high C4 recoveries in section B by maintaining higher pressure.

rl`he gasoline fraction is uncontaminated with the pump-around medium as described above and is condensed either in the tower by naphtha pump-back or in an external condenser, part of the naphtha being returned to the tower for fractionation. The number of plates to be provided in section B depends on the type of crude charged and the products desired. For the purposes of the present example, 2 plates may be used bett 'een the reduced crude inlet and gas oil withdrawal, 4 between gas oil and heating oil, 5 for stripling of gas fractions from the heating oil, 3 for naphtha-heating oil fractionations, and 1045 plates for the absorption of light eomponents in the top portion of section B.

As indicated in the drawing, final products may be recovered from tower 40 as follows. Gasoline of 400 F. end point amounting to about 35 to 45% on crude and having an octane rating of about -90 Research may be passed via line i0 to a conventional finishing stage ffii and then to tank 1122 to be blended therein with the hydroformate supplied via line 110. Gasoline may he recirculated by pump '7d via line '76 to section ii to serre as reflux. Final heating or light diesel oil may be re covered vie line 7d at a rate of about (L5-10% on crude. About 24% on crude of a heavy diesel oil stoel; may be obtained via line ed. A naphtha fraction somewhat heavier than that of the. gasoline in line et: and a boilin T range of, say, about 200 to 400 i?. may withdrawn from. a point intermediate between the withdrawal point of line 5d and the feed point of line be passed via line 29 to hydroformer 30 as described above. The amount of naphtha so withdrawn may vary between 0 and about 45% on crude depending on the proportion of virgin naphtha directly supplied to hydroformer 30 via line Z8.

Returning now to the combined reduced crude type bottoms withdrawn through line 2l, they may, if desired, be blended with gas oil or lighter fractions supplied through line 33 to adjust their viscosity to meet speci ications. The bottoms may then be cooled to about 20iie500 F. in cooler S5 and passed through to filtering facilities 90. Conventional sand filters, rotary or porous sintered ceramic filters may be used to remove from the combined residue all 'suspended or slurried solid catalyst hold-up of about 15-30 tons, and catalyst to oil ratios of about 3-l0, preferably about 5-7 by weight.

The advantages which render the system illustrated in Figure 2 particularly suitable for the present invention accrue chiefly from the described combination of the overflow principle with the provision of seal legs in the catalyst circulation pipes, preventing gas blow back and the dense phase riser 213 terminating closely below the bed level. These advantages are numerous and important. They include smaller line diameters and simpler mechanical construction of the solids circulation lines; the elimination of slide valves for controlling catalyst flow with attendant reduction in pressure drop tol about /o of conventional pressure drops and in maintenance requirements; reduction in vessel elevation by about 60%; re-

duced air pressure resulting in investment savings since at least 90% of the air passes directly to auxiliary burner 221 at a relatively low pressure; reduced size and cost of regenerator and reactor which may be shop fabricated rather than field fabricated; etc.

The temperature and pressure conditions specified in the above example for the operation of fraetionator 40, particularly of stripping section A are those best suited for the crude here specified. They may vary to a certain extent depending chiefly on the gravity of the crude charged, as will be readily understood by those skilled in the art. For example, for a lighter crude the temperature in the bottom of section A may be somewhat lower, and vice versa.

Another embodiment of the invention is illustrated in Figure 3 which, for the sake of simplicity, shows only those elements which diler in design and/or operation from those of Figures l and 1A, and in addition some of the pipe lines of Figures l and 1A to clarify the manner in which the equipment illustrated in Figure 3 is to be linked up with the combination unit described with reference to Figures 1 and 1A. In essence, the elements shown in Figure 3 are intended to take the place of hydroformer 30, stabilizer 100 and hydrogenators 116 and 118 of Figures l and 1A.

Referring now in detail to Figure 3, the system illustrated therein essentially comprises three catalytic hydroforrners 300, 302 and 304 connected in series, a hydroning stage 320 and a stabilizer-fractionator 330. The function of these elements in a combination unit of the type illustrated in Figures 1 and 1A will be forthwith described With reference to a platforming operation taking place in hydroformers 300, 302 and 304. lt should be understood, however, that other types of catalytic hydroforming may be carried out in this system in a substantially analogous manner.

ln operation, naphtha having a boiling range of about 150 to 400 F. may be passed through line 28 to hydrofoimer 300 via reheater 307 at a temperature of about 900 to 1000" F., a pressure of about 50 to 1000 p. s. i. g. and in an amount of, say, about l5 to 45% on crude. This naphtha may be supplied from crude still via line 10 and/or from tower 40 via line 29 in any desired proportion, as described with reference to Figures l and 1A. An amount of about 500 to 7000 s. c. f /bbL of recycle hydrogen is supplied to hydroformer 300 from line 306 at hydroforming pressure and a temperature of about 900 to 1200 F. Hydroforrners 300, 302 and 304 contain a platinum group catalyst such as platinum or palladium supported on alumina pellets preferably arranged in fixed beds. The naphtha-hydrogen charge passes in series through hydroformers 00, 302 and 304 and is reheated between stages in reheaters 300 and 310 to maintain similar temperatures in the three stages. Suitable platforming conditions to be maintained in hydroformers 300, 302 and 304 include temperatures of about 800 to l000 F., total pressures of about 400 to' 1000 p. s. i. g. and hydrogen recycle rates ot' about 3000 to` 12,000 s. c. f./bbl. At these conditions the octane number of the naphtha is improved anywhere from -60 points and the sulfur removed almost completely. The catalyst retains its activity for many months whereupon it may be replaced with fresh or regenerated catalyst, no continuous or frequent periodic regeneration being required.

The total effluent from the hydroforming or platforming stages passes through line 312 to hydroning stage 320. Simultaneously, hydroning stage 320 receives via line 119 all or any desired portion of the light gas oil range product fraction recovered from tower 40 prior to hydrogenation in hydrogenator 118. The combined charge is treated in hydroiining stage 320 with a hydroning catalyst such as oxides or suliides of Group V, VI and VIII metals at temperatures of about 500 to 800 F., pressures of about 50 to 1000 p. s. i. g. and throughputs of about 0.5 to 5 v./V./hr. At these conditions substantially complete conversion of undesirable constituents of the light gas oil fraction, such as sulfur compounds, etc. takes place by straight hydrogenation or hydrogen transfer from the platformate, without appreciably affecting the quality of the platformate. As a result of the high hydrogen partial pressure, catalyst deactivation by carbon deposition is relatively slow, eliminating the requirement of continuous or frequent periodic regeneration. Fixed bed operation is, therefore, suitable for hydrotining stage 320. However, any conventional continuous or periodic regeneration system involving iiuid or moving bed operation may be employed if desired.

The efliuent of hydrolining stage 320 is passed through line 322 to an intermediate section of conventional stabilizer-fractionator 330. This tower is so operated that a bottoms fraction of high quality heating or diesel oil my be recovered andpassed to tankage via line 332. platformate having a final boiling point of about 400 F. may be passed Via line 334 to blending tank 122 and gases containing about to 95% of hydrogen and amounting to about 5000 to 12,000 s. c. f. per bbl. are recovered overhead through line 336. About 500 to 1500 s. c. f. per bbl. of the gas in line 336 may be vented as excess. The remainder is recycled by means of recycle booster 340 via lines 338 and 342 and reheater 344 to line 306 and hydroformer 300.

Rather than supplying merely the product light gas oil fraction from line 119 to hydroning stage 320, any desired portion of the recycle stock from line rtrymay be used for this purpose. In this case, the oil fraction recovered through line 332 may be returned as a whole or in part to line 45 to serve as an upgraded recycle stock for cracking stage 50.

In all other respects, operation of the entire combination unit may be substantially as described with reference to Figures l and 1A, including operation of crude still l0, tower 40, cracking stage 50, coking stage 82, etc.

A third embodiment of the invention is illustrated in Figure 4 which is a schematical flow plan of a complete combination unit similar in various respects to that shown in Figures l and 1A, corresponding elements, though illustrated in a simplied manner, being identified by like reference numerals. An important additional element is a high pressure stripper 435 whose function will be forthwith described.

Referring now in detail to Figure 4, crude oil is charged via line 9 to crude still 10 and treated therein substantially as described with reference to Figure l. A kerosene or light gas oil fraction ready for use may be recovered via line 20. Light naphtha is withdrawn through line 16, heavy naphtha through line 18 and reduced crude through line 22. In addition, a gas oil fraction may be recovered through line 420 and passed wholly or in part to cracking stage 50 to serve as virgin cracking stock therein. Virgin gas oil may be recovered as product via line 421. Any desired proportion of the light and heavy naphthas may be recovered via lines 416 and 413 as product or passed directly to the bottom of tower 40 as described with reference toFigures 1, 1A and 3.

In accordance with a preferred 1modification -of vthis embodiment of `the invention, the heavy ynaphtha from still 10, amounting to about l to 20% on crude, `is passed to line 28 and hyd-roforming 'stage 30. 'The latter may be operated substantially as described for stage 30 and hydroformers 300, 302 and 304 with reference to Figures 1 and 3, recycle hydrogen being added via line 406 as will appear more clearly hereinafter.

The total Veffluent of hydroforming `stage 30 is passed substantially at the temperature and pressure of stage 30, say, at about '800-1000 F. and about 700-800 p. s. i. g. through line 432 to a bottom portion of high-pressure stripper 435. This stripper which lmay be of conventional design, having a lower disc-and-doughnut section C and an upper bubble tray section D, is maintained substantially at the pressure of reforming -stage 30.

Reduced crude from line 22 is passed by pump 437 through line 439 at the pressure of stripper 435 to the top of section C of stripper 435 which is so designed that the `temperature Ivaries from about 600 to 800 F. in the bottom to about 500 to 750or F. in the ytop of stripper 435. At these conditions, the reduced crude supplied through line 439 is stripped of its gas oil and lower boiling constituents to an extent of about 5-35% on reduced crude depending on the type of crude involved. The stripped reduced crude now amountingrto about 25 to 45% on crude is withdrawn through line 441 provided with pressure release valve 443 and passed to an upper portion of section A of tower 40, to be further stripped therein by cracked vapors supplied through line 52 from cracking stage 50 substantially as described with reference to Figures 1 and 1A.

A combined overhead containing the reduced crude strippings consisting chieliy of gas oil, the total hydroformate and the total hydrogen is withdrawn from strip-v per 435 via line 445, cooled in cooler 447 to about 80 to 120 F. and passed to gas liquid separator 449 substantially without pressure reduction other than that caused by cooling. The gas separated in separator 449, amounting to about 500 to 5000 s. c. f./bbl. and containing about 40 to 95% of hydrogen is withdrawn through line 406, reheated in reheater 451 to about 900 to 1200" F. and returned to hydroforming stage 30. Excess gas may be released through line 407 to be used as a fuel gas or in tower 40 as an additional stripping medium.

The total liquid separated in separator 449 may be passed through lines 453 and 455 provided with pressure release valve 457 to the fractionating sectionB of tower 40 to be fractionated therein substantially as described with reference to Figure 1A. If desired, part or all of the liquid in line 453 may be passed to a separate fractionator 460 after pressure release in valve 459. Product high quality hydroformate may be recovered overhead from tower 460 and recovered via line 462 to be blended in tank 122 of Figure 1A with finished gasoline from tower 40. A gas oil fraction may be withdrawn from tower 460 as bottoms va line 464 to be combined with the gas oil in line 42 and further treated as described with reference to Figures 1 and 1A.

' Similarly as explained with reference to Figures l, lA and 3, the virgin naphtha in lines 16 and/or 18 may be all or nfrt supplied directly to the bottom of tower 40 to serve t: a stripping medium for the reduced crude and corresponding Vamounts of similar fractions of tower 40 may be used as charging stock for hydroformer 30, as will be readily understood by those skilled in the art. Also,

. any desired portion of the virgin light naphtha in line 16 may be passed to'reforming stage 30.

The above description and exemplary operations have served to illustrate specific embodiments of the invention but are not intended to be limiting in scope.

What is claimed is:

1. In a combination crude distillation and hydrocarbon conversion process, the improvement which comprises subjecting crude oil to distillation in a distillation zone to produce `distillate fractions `including a gas oil fraction and a naphthacut and Vreduced crude, passing said reduced crude `to a low pressure product fractionation zone, catalytically lcracking said Igas yoil fractions and stripping said reduced crude in said product fractionation zone with vapors from said catalytic cracking operation subjecting a naphtha Vcut of said distillate fractions to catalytic reforming in a reforming zone yielding hydrogen, recovering stripped reduced crude bottoms from said product fractionation zone, withdrawing distillate fractions from said product fractionation zone and treating one of said `last named distillate fractions with said hydrogen outside said reforming and product fractionation zones.

2. The process of claim 1 in which said fraction treated with said hydrogen is a light gas oil withdrawn from said product fractionation zone.

^ 3. The process of claim l in which said fraction treated with said hydrogen is a heavy gas oil withdrawn from said product fractionation zone.

4. The process of claim 3 in which at least a portion of said treated heavy gas oilis subjected to cracking in a separate cracking zone and said reduced crude is stripped in said fractionation zone with products from said cracking zone.

5. The process of claim l in which at least a portion of said naphtha cutis passed from said distillation zone directly to said reforming zone.

6. The process of claim 1 in which at least a portion of said distillate fractions is passed from said distillation zone directly to said product fractionation zone to strip said reduced crude therein and a naphtha cut withdrawn from said fractionation zone is passed to said reforming zone to be reformed therein. Y Y

7. The process of claim l in which said distillate fractions consists essentially of heavy naphtha.

8. In a combination crude distillation and hydrocarbon conversion process, the improvement which comprises subjecting crude oil to distillation in a distillation zone to produce distillate fractions and reduced crude, passing said reduced crude to a low pressure product fractionation zone, stripping said reduced crude in said fractionation zone with vapors of at least a portion of said distillate fractions, subjecting a naphtha cut of said distillate fractions to catalytic reforming in a reforming zone yielding hydrogen, withdrawing an eiuent comprising hydrogen and reformed naphtha from said reforming zone, separating hydrogen from reformed naphtha, recycling a portion of said hydrogen to said reforming zone, separately Withdrawing a naphtha cut, light gas oil, heavy gas oil and stripped reduced crude from said fractionation zone, subjecting at least a portion of said heavy gas oil to catalytic cracking in a cracking zone, returning cracked products from said cracking zone to said fractionation zone to strip said reduced crude therein and treating at least a portion of said light gas oil with a portion of said hydrogen in a separate hydrogen treating zone.V Y

9. The process of claim 8 inwhich at leasta portion of said heavy gas oil is treated with a portion of said hydrogen in a separate hydrogen treating zone prior to being passed to said cracking zone. V

10. In combination crude distillation and hydrocarbon conversion process, the improvement which'Y comprises subjecting crude oil to distillation in a distillation zone to produce distillate fractions and reduced crude, passing reduced crude to a low pressure product fractionation zone, stripping said reduced crude in said fractionation zone with vapors of at least a portion of said distillate fractions, subjecting a naphtha cut of said distillate fractions to catalytic reforming in a reforming Vzone yielding hydrogen, withdrawing an effluent comprising hydrogen and reformed naphtha from said reforming zone, separately withdrawing naphtha, gas oil and stripped reduced crude from said fractionation zone, subjecting at least a portion of said gas oil to catalytic rcracking in a cracking zone, returning cracked products from said cracking zone to said fractionation zone to strip said reduced crude therein, treating hydrocarbon materials produced in said process with at least a portion of said hydrogen outside said fractionation and reforming zones and recycling a portion of said hydrogen to said reforming zone.

l1. r,A combination process for producing motor fuel which comprises fractionating crude petroleum oil in a distillation zone into a plurality of fractions including a reduced crude fraction, a gas oil fraction, a heavy naphtha fraction, and a light naphtha fraction, passing the reduced crude fraction to a stripping zone maintained under a relatively low pressure, catalytically hydroforming the heavy naphtha fraction in a hydroforming zone, stripping the reduced crude fraction in said stripping zone with gaseous products from said hydroforming zone and with at least a portion of the light naphtha fraction from said distillation zone, removing a stripped reduced crude fraction from said stripping zone, catalytically cracking the gas oil fraction from said distillation zone, passing the catalytically cracked vapors into said stripping zone to 18 act as additional stripping medium, fractionating vapors in said stripping zone to produce distillate fractions including motor fuel, and treating one of said distillate fractions from said stripping zone with hydrogen produced in said hydroforming zone in a zone separate from said hydroforming zone and said stripping zone.

12. The process according to claim 1l in which the catalytic hydroforming step is carried out at a temperature of about 800 to 1000 F., at a pressure of about 400 to 1000 p. s. i. g. and at hydrogen feed rates of about 3,000 to 12,000 standard cubic feet per barrel of naphtha to be reformed.

References Cited in the le of this patent UNITED STATES PATENTS 2,174,858 Keith, Jr Oct. 3, 1939 2,205,434 Phinney June 25, 1940 2,312,445 Ruthrut Mar. 2, 1943 2,366,218 Ruthruff Jan. 2, 1945 2,417,308 Lee Mar. 11, 1947 2,502,958 Johnson Apr. 4, 1950 

1. IN A COMBINATION CRUDE DISTILLATION AND HYDROCARBON CONVERSION PROCESS, THE IMPROVEMENT WHICH COMPRISES SUBJECTING CRUDE OIL TO DISTILLATION IN A DISTILLATION ZONE TO PRODUCE DISTILLATE FRACTIONS INCLUDING A GAS OIL FRACTION AND A NAPHTHA CUT AND REDUCED CRUDE, PASSING SAID REDUCED CRUDE TO A LOW PRESSURE PRODUCT FRACTIONATION ZONE, CATALYTICALLY CRACKING SAID GAS OIL FRACTIONS AND STRIPPING SAID REDUCED CRUDE IN SAID PRODUCT FRACTIONATION ZONE WITH VAPORS FROM SAID CATALYTIC CRACKING OPERATION SUBJECTING A NAPHTHA CUT OF SAID DISTILLATE FRACTIONS TO CATALYTIC REFORMING IN A REFORMING ZONE YIELDING HYDROGEN RECOVERING STRIPPED REDUCED CRUDE BOTTOMS FROM SAID PRODUCING FRACTIONATION ZONE, WITHDRAWING DISTILLATE FRACTIONS FROM SAID PRODUCT FRACTIONATION ZONE AND TREATING ONE OF SAID LAST NAMED DISTILLATE FRACTIONS WITH SAID HYDROGEN OUTSIDE SAID REFORMING AND PRODUCT FRACTIONATION ZONES. 